How do I introduce 2 guinea pigs? 10 points! Read the details carefully!?

Ok, so my daughter and her friend both have one guinea pig. They are both female, and they want them to be playmates. How do we introduce them? No, they will NOT be cagemates, the other guinea pig is staying for 1 week while my daughter's friend goes away for vacation. Give me step by step details!! 10 points are at stake!!